moebooru/lib/tasks/check_missing.rake

desc "find if there's any posts missing on file system"
task :find_posts => :environment do
  images_path = "#{Rails.root}/public/data/image/"

  Post.find(:all, :conditions => ["status != 'deleted'"], :order => "id DESC").each do |post|
    md5 = post.md5
    ext = post.file_ext
    path = "#{images_path}/#{md5[0..1]}/#{md5[2..3]}"
    file_name = "#{path}/#{md5}.#{ext}"
    puts "#{md5}.#{ext}" unless File.exist?(file_name)
  end
end